A. Rosová

Growth of High-Dielectric-Constant TiO2 Films in Capacitors with RuO2 Electrodes

Titanium dioxide thin films were grown on RuO 2 layers by atomic layer deposition. The stabilizing effect of the bottom rutile-type RuO 2 layer resulted in growth of the TiO 2 rutile films at temperatures above 275°C. Stabilization of the TiO 2 rutile phase occurred due to local epitaxial growth of the polycrystalline RUO 2 /TiO 2 /RUO 2 structure, as revealed by transmission electron microscopy. A dielectric constant as high as 155 and equivalent oxide thickness (EOT) as low as 0.5 nm were determined from the capacitance-voltage measurements for the TiO 2 films grown above 275°C. A leakage current density of 10 -3 A/cm 2 at 1 V bias voltage was obtained for the films with EOT equal to 0.5 nm.

Impact of plasma treatment on electrical properties of TiO2/RuO2 based DRAM capacitor

In this work, we systematically studied the influence of the plasma treatment (PT) on the structural and electrical properties of Pt/rutile-TiO2/RuO2 metal–insulator–metal capacitors. The leakage current of the 12 nm thick TiO2 dielectrics prepared by atomic layer deposition was reduced below 10−7 A cm−2 while the capacitance equivalent thickness was kept below 0.5 nm using oxygen PT of the bottom RuO2 electrode. Reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy analyses allowed the conclusion that O2 plasma smoothened the RuO2 surface and increased its oxygen content through plasma induced surface reconstruction. The nucleation of TiO2 on the plasma-treated surface was faster while the thickness of the capacitor dead layer at the TiO2/RuO2 interface was reduced.

Role of microtwins in twin lamella intersections and interconnections in YBa2Cu3O7−y

Abstract In YBa 2 Cu 3 O 7- y sets of microtwins, with twin spacing one order smaller than those of the principal twin lamellae, appear to relieve in areas of twin lamella intersections and interconnections strains caused by a contact of different orientation variants. Such microtwin sets cannot exist inside twin lamella intersections, so they grow in the vicinity of the intersections. In addition to microtwins also a twin boundary deformation is omnipresent to accomodate these strains. This causes the special morphology of twin lamella interconnections with widely spread residual strains.

Epitaxial YBa2Cu3O7 superconducting films, without twin planes on Y2O3/YSZ/Si

Abstract Epitaxial c -axis oriented YBa 2 Cu 3 O 7 superconducting thin films have been grown by off-axis sputtering on Si substrates covered with an Y 2 O 3 /YSZ buffer layer. The films show good superconducting properties and are crack-free for thickness as high as 120 nm. TEM observations reveal an epitaxial growth of YBCO on Y 2 O 3 with an angle of 45° between the [100] directions. Both layers display a microstructure which consists of slightly misoriented rectangular twin-free monocrystalline mosaic blocks.

Nanoscale Characterization of TiO2 Films Grown by Atomic Layer Deposition on RuO2 Electrodes

Topography and leakage current maps of TiO2 films grown by atomic layer deposition on RuO2 electrodes using either a TiCl4 or a Ti(O-i-C3H7)4 precursor were characterized at nanoscale by conductive atomic force microscopy (CAFM). For both films, the leakage current flows mainly through elevated grains and not along grain boundaries. The overall CAFM leakage current is larger and more localized for the TiCl4-based films (0.63 nm capacitance equivalent oxide thickness, CET) compared to the Ti(O-i-C3H7)4-based films (0.68 nm CET). Both films have a physical thickness of ∼20 nm. The nanoscale leakage currents are consistent with macroscopic leakage currents from capacitor structures and are correlated with grain characteristics observed by topography maps and transmission electron microscopy as well as with X-ray diffraction.

Fine-filamentary in situ?MgB2 wires

Nineteen-filament MgB2/Ti/Cu/SS composites have been made by an in situ approach using only drawing deformation to a filament size of 16.6?58??m. Circular cables containing 133 filaments were assembled from 1 + 6 strands of diameter 0.25?mm and 0.375?mm. All wires and cables were heat treated at 800??C/0.5?h in pure Ar atmosphere. The critical current densities Jc of the different wire sizes were measured and EDX element mapping was done for some of them. It was found that the critical current density decreases with reduced filament size, especially below the filament diameter of 27??m due to copper penetration through the thin Ti barrier ( 104?A?cm ? 2 was measured at 4.2?K and field 5.5?T for the thinnest 16.6??m filaments published up to now.

Superconducting films prepared by aerosol metal organic chemical vapour deposition on substrate with buffer layer

Superconducting films with a buffer layer were prepared by aerosol MOCVD on substrates. X-ray diffraction and high- resolution electron microscopy revealed a high degree of epitaxy of the heterostructure without any traces of interfacial reaction. Although both and films grow in a relaxed state, additional strain is incorporated into the structure during cooling from the deposition temperature, which results in a decrease of the lattice parameters perpendicular to the substrate surface. The films exhibit a critical temperature - 88 K with a critical current density of at T = 77.3 K. The angular dependence of the critical current at temperatures above 40 K in magnetic fields up to 0.5 T indicates that the films grown by aerosol MOCVD on the substrate behave as three-dimensional anisotropic superconductors.

Properties of in situ made MgB2 in Nb or Ti sheath

Pure Nb and Ti have been used as sheath materials for MgB2 wires examined experimentally. The reason for this research is to compare the effects of these metallic sheaths on the basic properties of MgB2 superconductor. Single-core SiC doped MgB2 wires with Nb and/or Ti sheaths have been made by a powder-in-tube in situ process. Different transport currents, phase compositions and grain connectivity were observed for Nb- and Ti sheathed MgB2 heat treated at temperatures 650–850u2009°C/30xa0min. It was found that the critical current density of MgB2/Nb annealed above 700u2009°C rapidly decreases, while Jc of MgB2/Ti is systematically increasing with temperature. This is explained by the positive role of Ti absorbing impurities from the MgB2 core and by the negative effect of boron diffusion into Nb, reducing the quantity and worsening the quality of the MgB2 core. The obtained results show clearly that a Ti sheath offers the application of higher heat treatment temperatures (above 700u2009°C) and consequently the achievement of higher critical current densities in comparison to MgB2/Nb.

Thermomechanical treatment, structure and transport currents in multicore Bi(2223)/Ag tapes

Abstract A set of 19 filament Bi(2223)/Ag tapes differing in thermomechanical treatment were analyzed structurally (XRD, SEM and TEM) and electrically by transport I c measurement in self field, in external magnetic field up to 1.2 T, and by I c -angular dependence, all at 77 K. The results obtained show that the optimal state for the application of a roll-sinter step is at the 2223/2212 phase ratio near to 1 (50% of 2223). The structural results (2223 phase content, grains morphology and texture) were studied, and they were related to the transport currents. I c (0 T), I c ( B ) and I c ( α ) as well as the n -exponent of current–voltage characteristics and its relation to I c are studied and discussed in connection with the structure induced by the thermomechanical treatment applied.

Properties of MgB2 wires made by internal magnesium diffusion into different boron powders

Different boron powders were used for MgB2 wires manufactured by internal magnesium diffusion. The structure of the MgB2 core, critical temperature and critical currents of Cu/Ti sheathed wires differing only in boron powder were analyzed and compared. It was found that the particle size and purity of boron powders influence the creation of the MgB2 phase and, consequently, also considerably influence its superconducting properties. The highest critical current density in the low external field was measured for wire with a boron purity of 98.5% produced by Pavezyum. It was used also for stabilized multi-core MgB2 wire with high engineering current densities in low magnetic fields at 20 K, which may be attractive for some low field applications, e.g. high-power wind generators.